Dynatron oscillator



Jan. 28, 1941.

.1. N. WHITAKER 2,230,097

DYNATRON OSCILLATOR V Filed Jan. 17, 1939 4 /3 I 3 b 1 2 11 7F OUTPUT 17ljlll I a 16- llNVENTdR MM ATTORNEY Patented Jan. 28, 1941 PATENT OFFICEDYNA'IIRON OSCILLATOR James N. Whitaker, Weehawken, N. J assignor toRadio Corporation of America, a corporation of Delaware ApplicationJanuary 1'7, 1939, Serial No. 251,304

3 Claims.

This invention relates to oscillators using the negative resistancecharacteristics of multi-element tubes. This type of oscillator iscommonly known as a dynatron oscillator. The circuit 5 arrangementsherein disclosed are particularly suitable for use in generatingultra-high frequencies, and also for frequency multiplication, ifdesired.

It is an object of my invention to provide a system for increasing theoutput of dynatron oscillators by lowering the plate impedance of thetube itself.

It is a further object of my invention to provide a system which permitsoscillations to be set up and maintained at considerably higherfrequencies than was heretofore considered possible, except at asacrifice of utilizable output energy.

My invention is an outgrowth from other inventions in the class ofoscillation generators such as illustrated in my Patents Nos. 2,067,365and 2,067,366 both granted January 12, 1937 and my Patent No. 2,103,655granted December 28, 1937. Certain improvements over the disclosures ofthese patents will now be explained in further detail, reference beingmade to the accompanying drawing the sole figure of which represents acircuit diagram of a preferred embodiment.

It is a well known characteristic of the dynatron oscillator that, whenoperating at a given frequency, its plate circuit load impedance must bemade very high with respect to the tube impedance in order to produceand sustain oscillations of any appreciable amplitude. Since it is quitediflicult to build up this load impedance to a proper value when workingat frequencies in excess of seven megacycles, it becomes necessary toobtain a proper tube load impedance match by resorting to otherexpedients than to increase the plate load impedance as far as one wouldlike. I have found that a solution to this problem is very muchfacilitated by proper design of the suppressor grid circuit so that thesuppressor grid receives a potential which is positive with respect tothe cathode. I have found, too, that it is quite essential that thesuppressor grid be isolated from the cathode for radio frequencycurrents.

Referring to the drawing wherein the complete circuit arrangement of apreferred embodiment of my invention is shown, the oscillator tube 6possesses a cathode I, a control grid 2, a screen grid 3, a suppressorgrid 4 and an anode 5. The input circuit connected between the cathodeand the control grid preferably includes a grid biasing source I and aninductive impedance 8. In

shunt with the biasing source and inductance is a piezo-electric device9 which provides suitable frequency stabilization. The cathode-to-anodecircuit includes a parallel-tuned circuit 10 which is resonant to thedesired frequency of output, whether it be the fundamental frequency ofthe oscillator or a frequency harmonically related thereto. A paralleltuned circuit [3 resonant to the fundamental frequency is shownconnected between the cathode I and the screen grid 3. This circuit istuned to the fundamental frequency of the oscillations generated. Screengrid potential is supplied from any suitable direct current source thepositive and negative terminals of which are indicated at 16. A blockingcondenser ll interconnects the cathode and the high potential side ofthe screen grid circuit. A potentiometer I 8 is provided across theterminals of the source l6 and is arranged with two adjustable taps l9and 20. Tap I9 is positioned so as to supply a potential to the anode 5which is intermediate between the potentials of the cathode and thescreen grid. The potentiometer tap 20 is adjusted to supply a suitablepotential to the suppressor grid 4 which is positive with respect to thecathode. Between the suppressor grid and the potentiometer tap 20 aninductive reactance member 2| is connected. This member serves toisolate the suppressor grid from the cathode for the high frequenciesthat are generated.

As in the systems of my prior patents above referred to, the oscillatoraction of the present system is obtained by virtue of the negativeresistance characteristic of the tube 6. The tube oscillations arelocked in step with those of the piezo-electric crystal 9 andoscillations are built up in the parallel tuned circuit It] at theharmonic frequency to which it is tuned. The oscillations are sustainedby virtue of regenerative action, capacitive feed-back occurring betweenthe screen grid 3 and the control grid 2. If desired, this capacitivefeed-back may be augmented by connecting a small capacitor ll betweenthe screen grid and'the control grid, though this is not alwaysdesirable in ultra-high frequency work.

The particular embodiment of my invention herein illustrated lendsitself to operation at a wide range of frequencies. The plate impedanceof the tube 6 is not so great as one might expect it to be for theultra-high frequencies which the tube is capable of generating. Due tothis relatively lower plate impedance the amplitude of the oscillatoryoutput energy is relatively high. This is a particularly desirablefeature where frequency multiplication is obtained, since, for the 5ative to said second grid.

higher harmonics it will be understood that high power output from sucha generator is difficult at best. In this case there is a minimum ofreaction between the load circuit impressed across the capacitors l2 andI4 and the fundamental frequency oscillator circuit of the tube.

The particular circuit arrangement as illustrated may readily bemodified for use in such circuits as are disclosed in my prior patentsabove referred to. It is also possible under certain conditions tocouple the suppressor grid 4 to either the screen element 3 or the anode5. Such modifications may be adopted in accordance with the operationfrequency and with the particular load requirements imposed upon theoscillator.

I claim:

1. An oscillation generator comprising a discharge tube having acathode, a control grid, a second grid, a suppressor grid and an anode,a piezo-electric crystal and a tuned circuit regeneratively connectingtogether said cathode, control grid and second grid, a resonant circuitinterconnecting the anode and cathodeand arranged to be tuned at timesto the fundamental frequency of the oscillations generated and at othertimes to a harmonic of said fundamental frequency, means for maintaininga positive bias on said suppressor grid with respect to the oathode,means including a high reactive impedance interposed between saidsuppressor grid and the cathode for isolating said grid at thefundamental frequency of oscillations, and means for maintaining a biaspotential on said anode which is positive relative to the cathode andnegative rel- 2. An oscillation generator and frequencymultipliercomprising an electron discharge tube having a cathode, a control grid,a screen grid, a suppressor grid and an anode, a direct current sourcein circuit between the cathode and the screen grid, means for impressingupon said an ode a direct current potential which is intermediatebetween the potentials of the cathode and screen grid, a resonantcircuit connected between the cathode and screen grid, resonating meansconnected between the cathode and control grid, both the resonantcircuit and the resonating means being tuned to the frequency to begenerated, means for impressing upon said suppressor grid a positivebias and upon the control grid a negative bias, both with respect to thecathode, means including a highly inductive impedance in circuit betweensaid suppressor grid and the oathode for isolating the suppressor gridat the frequency to be generated, a resonant circuit connected betweenthe anode and cathode and tunable alternatively to the frequency to begen-y erated and to a desired frequency harmonically related thereto.

3. An oscillation generator and frequency multiplier comprising adischarge tube having a cathode, an anode and a plurality of gridsarranged progressively between the cathode and anode, a fundamentalfrequency control circuit including a piezo-electric device between thecathode and the grid adjacent thereto, a circuit resonant to saidfundamental frequency and interconnecting the cathode and anintermediate grid, a circuit resonant to a harmonic frequency andinterconnecting the cathode and anode, a direct current biasing andoperating means having connections to the several electrodes of saidtube, said means comprising a direct'current source and a potentiometeradapted to render both the anode and the grid adjacent thereto morepositive than the cathode, and to maintain said intermediate grid morepositive than the anode, thereby to produce dynatron action in saidtube, means to isolate the grid adjacent the anode with respect to thehigh frequency currents traversing thecathode, and means to deliver aharmonic frequency output from the cathode-to-anode circuit.

JAMES N. l/VHITAKER.

